9. Euphorbia glyptosperma Engelm. (sand mat, rib-seeded sand mat)

Chamaesyce glyptosperma (Engelm.) Small

Map 1671, Pl. 381 a, b

Plants annual, with taproots. Stems 5–40 cm long, prostrate, several- to many-branched, the branches often overlapping (plants mat-forming), not flattened toward the tip, yellowish green to tan, often pinkish- to purplish-tinged, glabrous, sometimes slightly glaucous. Leaves opposite, sessile or very short-petiolate. Stipules small scales 0.3–1.0 mm long, these not fused, mostly irregularly fringed or lobed. Leaf blades 3–15 mm long, oblong to oblong-obovate or oblong-ovate, asymmetrical at the base with the side toward the stem tip usually angled and the other side rounded to shallowly cordate and expanded into a small, rounded auricle, more or less rounded at the tip, the margins minutely few- to several-toothed (best observed with magnification), the surfaces glabrous, sometimes reddish-tinged or with an irregular reddish spot, the undersurface usually pale grayish green. Inflorescences axillary, of solitary cyathia or appearing as small clusters on short axillary branches. Involucre 0.6–0.9 mm long, glabrous, the rim shallowly 4-lobed or 4-toothed, the marginal glands 4, 0.1–0.3 mm long and more or less equal in size, the body narrowly oblong, greenish yellow, with a relatively inconspicuous petaloid appendage 0.1–0.4 mm long, this white or pinkish-tinged, the margin usually irregularly notched. Staminate flowers 1–5 per cyathium. Ovaries glabrous, the styles 0.1–0.4 mm long, each divided 1/3–1/2 of the way from the tip into 2 somewhat club-shaped lobes. Fruits 1.2–1.8 mm long, glabrous. Seeds 1.0–1.4 mm long, oblong-ovate in outline, angular in cross-section, flat to slightly convex at the base, the surface with 3 or 4(–6) coarse transverse ridges (these mostly extending the full width of the face and through the angles), white to light tan, lacking a caruncle. June–October.

Uncommon, mostly in counties along the Missouri and Mississippi River floodplains (U.S. [except most southeastern states]; Canada, Mexico). Banks of streams and rivers, sand prairies, and loess hill prairies; also roadsides and open, disturbed areas.